Ship safety at sea has many aspects, of which sufficient intact stability lets the ship to maintain its upright position in wind and waves. Sufficient intact stability is in practice often related to cargo safety, but ultimately also to the safety of the whole ship. A sudden capsize in seaway tends to lead to accidents with no survivors, because the capsize process in such a case is too fast for an orderly evacuation to be executed onboard the rapidly heeling ship.

If the watertight integrity of the ship is lost, usually as a consequence of an accident, the damage stability of the ship in seaway becomes important. Straightforward ship sinking is often slow enough for orderly passenger and crew evacuation, whereas capsize of a damaged ship can happen very rapidly leading to very low passenger and crew survival rate. The most notorious accidents with a high number of human lives lost belong to this category.

The most common reasons for the loss of the watertight integrity are collisions with other ships, groundings, and in some cases also sea or ice loads. Thus also good manoeuvrability of the ship is important for its safety, especially in congested traffic routes or restricted waters.

International regulations require minimum standards for many aspects of ship safety. Often these requirements are sufficient. Parametric rolling of certain types of modern ships is an issue where a direct approach is still needed. Therefore frequent calculations and testing are carried out.

The HSVA carries out model testing and numerical investigations on ship intact and damage stability. In the past many of the investigations served the purpose of accident investigations or the purpose of international stability rule development.

In the HSVA various tests and calculations related to safety issues varying from manoeuvring and dynamic course stability problems in calm water to ship behavior in seaway and in ice covered waters are routinely carried out.